Scientific Forecaster Discussion
fxus66 klox 250403
Area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
903 PM PDT sun Mar 24 2019
Mostly sunny skies are expected on Monday with warming
temperatures. A weak cold front will move into the area Monday
night into Tuesday bringing increasing clouds and a chance for
rain north of Point Conception. Another front moves in Tuesday
night into Wednesday bringing a chance of rain across the area.
Short term (sun-wed)...24/901 PM.
The latest satellite imagery indicates a ridge of high pressure
over the Gulf of California this evening with an axis moving east
over Southern California and Nevada. A broad trough of low
pressure is centered is spinning counterclockwise over the eastern
Pacific Ocean about 1400 miles northwest of Los Angeles, or near
42n and 140w. Ridging aloft will slowly move east tonight while
the broad trough will slowly approach the West Coast through
Surface pressure gradients, near neutral to slightly onshore this
evening, should trend more onshore over the coming days as the
trough approaches the West Coast. Patchy dense fog could develop
for portions of the area tonight as surface gradients are near
neutral. The highest likelihood would place patchy dense fog near
the Los Angeles County coast on Monday morning around daybreak,
but patches of dense fog cannot be ruled for the Ventura County
coast either. For now, the forecast has been trended toward the
more likely scenario.
***From previous discussion***
A surface front associated with the broad trough moving through
the eastern Pacific will weaken as it moves into slo County and
northern sba County Mon night and Tue. Rainfall with this dying
front is expected to be one tenth of an inch or less Mon night and
Tue, except one quarter to one half of an inch across
northwestern slo County. Clouds will increase across l.A./Vtu
counties Mon night and Tue. Max temps should be down a few degrees
in most areas on Tue.
Next cold front expected to bring rain threat to southwest
California Tuesday night through Wednesday night, with highest
probabilities and amounts favoring San Luis Obispo and northern
Santa Barbara counties. Rain chances begin across San Luis Obispo
and Santa Barbara counties on Tuesday night, spreading into
Ventura and la counties on Wednesday. Current 12z model runs and
ensemble forecasts trending higher with rain chances for areas
north of Point Conception, so have trended pops upward accordingly
for these areas. Rainfall amounts are expected to range between
0.25 and 0.50 inches for San Luis Obispo and Santa Barbara
counties, with local totals up to 1 inch across the foothills of
northwest San Luis Obispo County (near Hearst castle). For
Ventura and la counties, rainfall amounts will generally range
between 0.10 and 0.25 inches, with locally higher totals possible
in the western Ventura mountains. Snow levels will generally range
between 6000 and 6500 feet Tuesday night into Wednesday, then
lower to between 4500 and 5000 feet Wednesday night.
Long term (thu-sun)...24/155 PM.
On Thursday, some lingering low level moisture will bring partly
cloudy and cool conditions with a slight chance of morning
showers to areas north of Point Conception. Beyond Thursday,
models still exhibiting some differences with respect to ridging
across the region. The ec shows an amplifying ridge with dry
weather and a warming trend Fri and Sat, with Max temps climbing
into the 70s in the valleys and some coastal areas. The GFS is
farther west with an upper low dropping through the Great Basin
and rockies Fri and Sat, and as a result shows much less in the
way of warming. Have hedged a bit toward the ec model as it has
been a bit more consistent later in the week.
At 23z, the marine layer depth was around 500 feet deep. The top
of the inversion was around 1050 feet with a temperature near 13
VFR conditions are expected throughout the period, except for a
chance of sub-VFR conditions at coastal and valley terminals after
08z through 18z.
Klax...VFR conditions are expected throughout the period, except for a
40 percent chance of IFR to MVFR conditions between 08z through
17z. Any east winds will remain less than 7 knots.
Kbur...VFR conditions are expected throughout the period, except for a
30 percent chance of IFR to MVFR conditions between 08z through
For the outer waters, moderate to high confidence in current
forecast. Small Craft Advisory (sca) conditions due to high seas
will be allowed to expire as of 9 PM this evening. For Monday and
Monday night as well as Tuesday afternoon, there is a 40 percent
chance of Small Craft Advisory level southerly winds across the northwest portion of the
northern zone (pzz670), 20% for (pzz673). On Thursday into
Thursday night, there is a 60 percent chance of Small Craft Advisory level
northwest winds across the southern two zones of the outer
waters, then across all of the outer waters by Friday.
For the inner waters north of Point Sal, moderate to high
confidence in current forecast. Conditions are expected to remain
below Small Craft Advisory levels through Wednesday. Thursday and Friday, there is
a 40 percent chance of Small Craft Advisory level west to northwest winds during
the afternoon and evening hours.
For the inner waters south of Point Conception, high confidence
in current forecast through Wednesday, with conditions below Small Craft Advisory
levels. There is a 40 percent chance of Small Craft Advisory level winds across
the inner waters Thursday afternoon and evening and possibly into
California...high surf advisory in effect until 8 am PDT Monday for zones
34-35-40-41-87. (See laxcfwlox).
Hazard potential outlook (wed-sun).
A storm system could bring rain and high Elevation Mountain snow
to the region between Tuesday night through Wednesday night.
Gusty winds are possible with this storm, especially in the
mountains. High surf is possible late Wednesday.